Healing of wound with negative pressure is today an accepted method for treating difficult and with earlier conventional methods slow-healing wounds.
Drainage of, for example, surgical wounds or other weeping wounds with negative pressure is a standard treatment which has been used for decades. An example of a manual suction pump for this purpose is described in U.S. Pat. No. 3,742,952.
U.S. Pat. No. 3,572,340 describes a pump in the form of an elastically compressible body made of an open-celled foam material, preferably a polyurethane foam, which body also serves as a receptacle for fluid drained from the wound. The pump is said to have a capacity to maintain an negative pressure of 15-80 mmHg for more than 48 hours. A perforated drain is intended to be placed in the wound pocket and is connected to the pump by a tube. A similar device is described in U.S. Pat. No. 4,525,166, in the description of which it is specifically stated that the negative pressure not only drains wound fluid but also draws together the wound edges and stimulates tissue growth and healing of the wound. The two latter publications therefore state that vacuum treatment of wounds stimulates wound healing.
The terms vacuum treatment, treatment with reduced pressure and treatment under negative pressure are used interchangeably in the literature. It should be pointed out that, where these terms are used within this description, treatment at a pressure below normal atmospheric pressure is always meant.
Deep wounds have also been treated with a combination of a rinsing fluid supply and subsequent aspiration. Examples of such devices are described in U.S. Pat. No. 5,358,494 and U.S. Pat. No. 4,382,441.
Extensive studies of the effect of both continuous and intermittent treatment of wounds under negative pressure, i.e. pressure below normal atmospheric pressure, were conducted during the 80's in Russian institutions. It was here demonstrated that slow-healing wounds heal substantially faster with the aid of vacuum treatment compared with conventional treatment methods. It was also shown, inter alia, that treatment with reduced pressure produced a significant antibacterial effect. The said Russian studies are described in articles in the Russian medical journal Vestnik Khirurgii. The articles from the said journal are:    1) Kostiuchenok et al, September 1986, pages 18-21.    2) Davydov et al, September 1986, pages 66-70.    3) Usupov et al, April 1987, pages 42-45.    4) Davydov et al, October 1988, pages 48-52.    5) Davydov et al, February 1991, pages 132-135.
In an article by Chariker et al in the journal Contemporary Surgery, issue 34, June 1989, it is stated that vacuum treatment improves the growth of granulation tissue and the wound contraction of wounds which with conventional treatment are very slow-healing.
Vacuum treatment of wounds is described in for instance U.S. Pat. No. 4,969,880, U.S. Pat. No. 5,645,081, U.S. Pat. No. 5,636,643, U.S. Pat. No. 6,855,135 and WO 2006/025848 A2.
In order to get a good wound healing when using negative pressure treatment it is important to control the pressure at the wound, i.e. that the chosen and set pressure of the system is the same as is achieved at the wound.
The therapy pressure, i.e. the pressure at the wound, is affected by several factors, such as the difference of the height levels of the wound and of the canister when there is a liquid column in the suction tube between the wound and the canister. The tube can also be clogged by exudates with high viscosity.
EP 0 865 304 B1 describes an apparatus that in addition to a drainage conduit between the wound cover and the canister includes an additional conduit connecting the wound cover to a pressure detecting means, whereby the pressure substantially at the wound site can be measured. The apparatus according to EP 0 865 304 B1 describes an embodiment which includes a relief valve for admitting ambient air to the wound site via the additional conduit and means for controlling the operation of said relief valve.